People have tried to harness wind energy for thousands of years. Lately, with fossil fuels running out, techniques for converting energy in the wind to other forms of energy and, in particular, electrical energy have become more popular. It is known to use wind turbines to extract the energy from the wind. It is also known to use kites to extract energy from the wind. Kites can fly at high altitudes where wind speeds are more reliable than the wind speed at the height of the hub of a wind turbine. The hub height of a wind turbine may be at 80 or 100 m whereas kites can be flown at a typical height of 400 to 700 m or even higher. With kite-based power generating systems, the majority of the mass is kept near to ground or water level at a base station, thereby minimising bending moments and reducing the mass of the airborne equipment considerably. Repair and service of the equipment is easier since the bulk of the equipment is at low-level. At sea, the ground based equipment can be mounted on towable barges or buoys allowing retrieval to harbour for major repair or service.
A system for the extraction of energy from the wind using a kite typically includes a kite connected to a base station using a tether. The tethers used in kite-based power generating systems undergo considerable stress during operation due to the relatively high forces involved. It is necessary to replace exhausted tethers once they have deteriorated. The maintenance thus required has a cost in terms of time when the system is not in use as well as a financial cost. The invention was devised in this context.